Prostanoid EP4 receptor is a G protein-coupled receptor that mediates the actions of prostaglandin E2 (PGE2) and is characterized by the longest intracellular C terminus loop when compared to other prostanoid receptors. Mainly, EP4 receptors couple to G proteins and mediate elevations in cAMP concentration, although they do participate in other pathways as well. There are some redundancies in function between EP2 and EP4 receptors. For example, both receptors induce PGE2-mediated RANKL through cAMP. However, EP2 receptors are involved in cumulus expansion in ovulation and fertilization, whereas EP4 regulates closure of the ductus arteriosus. Expression of EP4 receptors is controlled by various physiological and pathophysiological processes as these receptors participate in ovulation and fertilization, induce bone formation, protect against inflammatory bowel disease, facilitate Langerhans cell migration and maturation and mediate joint inflammation in a model of collagen-induced arthritis, among others.